TECHNETIUM COMPLEXES WITH THIOETHER LIGANDS .3. SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF CATIONIC NITRIDOTECHNEIUM(V) COMPLEXES WITH THIACROWN ETHERS

The first representatives of a new class of TcN complexes with thiacro wn ethers have been prepared by ligand exchange reaction of NBu(4)[TcN Cl4] with 1,4,8,11-tetrathiacyclotetradecane (14S4), 1,5,9,13-tetrathi acyclohexadecane (16S4), 1,5,9,13-tetrathiacyclohexadecane-3, 11-diole (16S4-(OH)(2)) and 1,4,7,10,13,1 6-hexathiacyclooctadecane (18S6). Th e crystal structure of [TcNCl(14S4)]TcNCl4 (1) consists of couples of independent cations with the metal in the oxidation state +5 and hexav alent TcNCl4- anions. In the complex cation the metal is six-coordinat ed in a rather distorted octahedral geometry, being directly bound to four sulphur atoms from the macrocyclic ligand in the equatorial plane and to the nitrido atom and to one chlorine atom in the axial positio ns. The strong trans influence of the nitrido ligand causes an extreme lengthening of the Tc-Cl bond distance to 2.718 Angstrom. The octahed ral molecular structure of [TcNCl(18S6)]TcNCl4 (3) is comparable with that of 1, but only four sulphur atoms of the thiacrown ether form the equatorial plane, two sulphur atoms remain non-coordinated, and the n itrido and Cl- ligands are in axial positions. The most interesting fe ature in the structure of [TcNCl(16S4-(OH)(2))]Cl (5) is the observati on of an exceptionally long Tc-N distance of 1.95 Angstrom.